The present invention relates to pectin degrading enzymes, in particular to enzymes with polygalacturonase activity. More particularly, it relates to fungal enzymes with polygalacturonase activity, to polynucleotides encoding these enzymes and to the use of these enzymes in the food and feed industry.
Pectins are major constituents of the cell walls of edible parts of fruits and vegetables. The middle lamella which are situated between the cell walls are mainly built up from protopectin, the insoluble form of pectin. Due to their colloid nature, pectins have an important function in the water regulation of plants.
Pectins are composed of a polygalacturonic acid backbone in which 1,4-linked alpha-D-galacturonan chains (smooth regions) are interrupted at intervals by the insertion of 1,2-linked alpha-rhamnopyranosyl residues (hairy regions) (Pilnik et al. (1970) In: The Biochemistry of fruits and their products, 1, 53). A varying proportion of the carboxyl groups of the polymer may be esterified with methyl groups.
Pectin degrading enzymes are important tools in the food industry, especially in the fruit and vegetable (processing) industry. Aspergillus niger and other fungi produce a whole range of enzymes which can advantageously be used in the degradation of the pectin polymer. Examples of such enzymes are pectin (methyl)esterase, which can remove the methyl group from the pectin, while leaving the pectin backbone intact; pectin lyase and polygalacturonases, which disintegrate the pectin backbone.
In the food industry there is sometimes a need for the individual enzyme (e.g.pectin esterase for gellification) and sometimes a need for the combined action of the different enzymes (e.g. pectin esterase plus polygalacturonase for liquefaction of plant material). Heldt-Hansen et al. (In: Pectins and pectinases, J. Visser and A. J. G. Voragen, (editors) 1996, Elsevier Science B.V.), for instance, describe how purees may be obtained by either a combination of polygalacturonase and pectin lyase, or a combination of polygalacturonase I, rhamnogalacturonase B and rhamnogalacturonase A, or a combination of pectin lyase, rhamnogalacturonase B and rhamnogalacturonase A.
These pectinases may be isolated from various microorganisms, but it is often not possible to obtain the desired enzymes in desired ratios. On the other hand, the availability of cloned pectinases allows for the preparation of tailor-made enzyme mixtures.
One of the pectinases which has been cloned is the group of polygalacturonases, which disintegrate the pectin backbone of de-esterified pectin by depolymerisation.
He et al. ( J. Bacteriol. 172, 4988, (1990)) describe the cloning of an exo-polygalacturonase from Erwinia chrysanthemi. 
WO 94/14952 describes three enzymes with endo-polygalacturonase activity which are obtainable from Aspergillus aculeatus. 
EP 0 421 919 describes an enzyme with polygalacturonase activity which is obtainable from Aspergillus niger. 
EP 0 388 593 describes the expression of an endo-polygalacturonase from Aspergillus niger. 
There is still a need for pectin-degrading enzymes with new properties, which are a useful addition to the existing range of pectinases.